A senior civil servant has told chief constables to end public debate on what many top officers see as the creeping centralisation of Scottish policing.

Bridget Campbell, the official in charge of police and community safety at the Scottish Government, sparked outrage by saying open discussion on the future role of a new centralised support agency was "unhelpful".

Her remarks, in a letter to the chief constables and boards of Scotland's eight regional forces, come as police chiefs become increasingly concerned about what one insider called "landgrabbing" by the Scottish Police Services Authority (SPSA).

The Herald yesterday revealed that one of the government's most senior advisers believed the SPSA, which was set up last year by the old Labour-Liberal coalition, should take over key roles, such as serious fraud, counter terrorism and motorway policing.

Scotland's biggest force, Strathclyde, has the most to lose from any SPSA expansion. Its new chief constable, Steve House, has made it clear he believes transferring functions from his force to the SPSA would hurt frontline policing.

Ms Campbell in her letter, which was written before yesterday's revelations in The Herald, said: "I think that further public debate about these matters would be unhelpful."

Mr House, speaking at Strathclyde's ruling joint police board yesterday, made it clear that he had no intention of biting his tongue.

Referring to Ms Campbell's letter, he said: "They wish the debate to take place behind closed doors. I don't think that is appropriate. Silence is taken as acquiesence, I am afraid.

"Effectively the SPSA is being promoted as a national solution for policing in Scotland. It is a solution for the seven other forces, not Strathclyde, because our services will get worse. We can't accept that."

SPSA has already taken over control of all forensic science in Scotland. Senior officers openly say they are still not happy with the quality of that service. The authority also oversees the Scottish Crime and Drug Enforcement Agency and criminal records and, from April 1, will take over IT for all eight forces.

Mr House won full backing for his position from his board and its convener, Paul Rooney, a Labour councillor from Glasgow.

"I am pleased the chief constable is taking a stance on this," Mr Rooney said.

Ms Campbell's letter angered several members of the board. Christopher Mason, a Glasgow Liberal Democrat, said: "I have never before known a civil servant try to tell people, including elected members, that they must stop a public debate. It is extreme arrogance, I think.

"In fact, there is an urgent need for an extended public debate about these issues."

A spokesman for the Scottish Government said: "Of course there will be debate about the right way forward. We welcome that. But decisions on whether SPSA should have additional functions in the future will be for ministers in consultation with the Association of Chief Police Officers in Scotland (Acpos) and police boards. There are already well-understood channels for that consultation."

The SPSA also said it was happy to see its role thrashed out in public.

Its chief executive, David Mulhern, said: "SPSA brings one of the biggest changes in how we provide policing services to the Scottish community in over 30 years.

"As our organisation develops we welcome feedback and encourage debate on the future direction of support services for Scottish policing."

Peter Wilson, Chief Constable of Fife and Honorary Secretary of Acpos, said: "We welcome the fact that mech- anisms are being put in place through which consideration can be given to the question of further transfer of functions to the SPSA."